Excavation rounded off for Maastricht A2 tunnel section

20 May 2014

The building pit for the new double-decker tunnel that will lead the A2 through Maastricht is now fully excavated. It will be the first tunnel in Europe with two stacked pairs of tunnel tubes for cars and trucks.

After working for over two years, the excavation of the building pit – with a total length of over 2 km – has presently been rounded off. Over 1,400,000 m³ of earth, gravel and marl have been dug up and carried off. During the apex of the excavation project, the team deployed over 450 trucks. If we were to line up all the trucks that were involved in the operation, the row would extend 1,000 km – from Maastricht to Marseille. The aim is to take the new tunnel into operation in late 2016.

Dry building pit

By Dutch standards, the large building pit at Maastricht – which has a maximum depth of 22 m and a length of over 2 km and required the contractor to first pump off the groundwater – is quite unusual. The solid Limburg soil allowed the contractor to construct a ‘dry’ excavation pit. This underground operation yielded some fantastic pictures:

Usually, these projects are realised on the basis of a ‘wet excavation pit’. This involves digging out the building pit from ground level, after which the contractor pours an underwater concrete flooring. As soon as this tunnel floor has cured, the workers can proceed to pump out the groundwater and rainwater.

Unique characteristics

The Maastricht project involved the high-paced excavation of a gigantic volume of earth – in an urban environment where the team had to consistently make the most of the limited space available. The local soil is a lot firmer than in the Northern Netherlands, and also has unique characteristics such as different geological faults and a range of varying-density marl layers, alternated by rock-hard layers of flint and karst features (soil cavities). This is why the team made a thorough advance study of the local soil characteristics, and closely monitored the building pit and the surrounding area during the excavation via the so-called ‘Observational Method’. This method comprises a variety of tracking and safety systems that can be used to monitor the status of, for example, the sheet pile retaining walls, the shoring struts and the groundwater level in the pit, the surrounding built-up area and the temporary road constructed alongside the building site. The steel sheet piles make sure that the excavation pit’s walls are structurally sound. Shoring struts, the interpositioned steel tubes, keep the piles in place. Click below for aerial footage of the new tunnel section:

On our way to the final phase

While the excavation was still underway, the team also started pouring concrete. The objective is to round off the concrete carcassing by early 2015. After this, the workers will proceed to complete the fabric. The final phase has been reserved for the installation and testing of the hard- and software for the traffic and tunnel engineering systems. In the near future, these systems will ensure that the tunnel’s safe day-to-day operation. In addition, the emergency services that will be dealing with the tunnel after it becomes operational still need to receive special training. A so-called ‘ready-to-operate’ team has already started working for this final phase.

After the tunnel: new additions to the city

Besides the A2 tunnel, the current project also involves the realisation of 21 new structures in and around Maastricht, including a number of smaller tunnels, viaducts, fly-overs and a bridge. Together, they constitute a major upgrade for the city’s infrastructure and significantly improve the accessibility of both Maastricht and the surrounding region. In parallel, the team will start preparing the ground-level redevelopment of the tunnel corridor. Ultimately, the A2 Maastricht project is intended to also yield a new district to the east of the old centre. The development contract runs until 2026. The total investment involved in the A2 Maastricht project amounts to some EUR 1 billion.

This joint press release is issued by the A2 Maastricht Steering Committee.